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Abstract:

A method detects a lack of driver activity at the steering wheel of a
motor vehicle. A moment imparted by hand to the steering wheel by the
driver is repeatedly measured, and if in a plurality of successive
measurements the magnitude of a value of the moment imparted by hand does
not exceed a threshold value, a lack of driver activity is inferred. The
magnitude of the threshold value is dependent on the surface condition,
in particular on the degree of unevenness, of the roadway being traveled
upon. The degree of unevenness of the roadway may be derived from a
measured vertical acceleration in the wheel suspension of the vehicle or
from deceleration and/or acceleration signals of at least one wheel of
the vehicle.

Claims:

1. A method of detecting a lack of driver activity at a steering wheel of
a motor vehicle, the method comprising the acts of: repeatedly measuring
a moment imparted by hand to the steering wheel by a driver; in an event
that in several successive measurements a magnitude amount of the moment
imparted by hand does not exceed a threshold value, inferring a lack of
driver activity, wherein an amount of the threshold value is a function
of a surface condition of a road being traveled on.

2. The method according to claim 1, wherein the surface condition is a
degree of unevenness of the road

3. The method according to claim 2, wherein the degree of unevenness of
the road is derived from a measured vertical acceleration in a wheel
suspension of the vehicle.

4. The method according to claim 2, wherein the degree of unevenness of
the road is derived from at least one of deceleration and acceleration
signals of at least one wheel of the vehicle.

5. The method according to claim 1, wherein: the amount of the measured
moment imparted by hand is used as a first magnitude of the moment
imparted by hand; a gradient of the moment imparted by hand is taken into
account as a further magnitude of the moment imparted by hand; and only
in an event that, in several successive measurements, the amount of the
first magnitude of the moment imparted by hand does not exceed a first
threshold value dependent on the road condition as well as that the
further magnitude of the moment imparted by hand does not exceed a second
threshold value provided for said magnitude, is the lack of driver
activity inferred.

6. The method according to claim 1, wherein a length of a time period
within which several successive measurements of the moment imparted by
hand are carried out before, in an event of a lasting falling below the
threshold value, a lack of driver activity is inferred, is a function of
the driving speed of the vehicle.

7. The method according to claim 5, wherein, in an event that at least
one of possible considered magnitudes of the moment imparted by hand
exceeds an assigned minimal value, a new series of successive
measurements of the moment imparted by hand is started, so that preceding
measurements are not taken into account for detecting the lack of driver
activity.

8. The method according to claim 7, wherein a new series of successive
measurements of the moment imparted by hand is started only if one of the
magnitudes of the moment imparted by hand continuously exceeds its
assigned minimal value during a defined time period.

9. The method according to claim 7, wherein an amount of the minimal
value and/or of the defined time period is a function of the surface
condition.

10. The method according to claim 8, wherein an amount of the minimal
value and/or of the defined time period is a function of the surface
condition.

11. The method according to claim 10, wherein the surface condition is a
degree of unevenness of the road.

12. The method according to claim 9, wherein the surface condition is a
degree of unevenness of the road.

Description:

CROSS REFERENCE TO RELATED APPLICATIONS

[0001] This application is a continuation of PCT International Application
No. PCT/EP2011/063100, filed Jul. 29, 2011, which claims priority under
35 U.S.C. §119 from German Patent Application No. DE 10 2010 039
949.3, filed Aug. 30, 2010, the entire disclosures of which are herein
expressly incorporated by reference.

BACKGROUND AND SUMMARY OF THE INVENTION

[0002] The invention relates to a method of detecting a lack of driver
activity at the steering wheel of a motor vehicle, wherein the moment
imparted by hand to the steering wheel by the driver is repeatedly
measured, and in the event that in several successive measurements the
amount of the magnitude of the moment imparted by hand does not exceed a
threshold value, a lack of driver activity is inferred. With respect to
the state of the art, reference is made, in particular, to German Patent
document DE 10 2008 021 150 A1, and further in the course of the
following description, to German Patent documents DE 34 21 253 C2 and DE
10 2005 014 237 A1.

[0003] In DE 10 2008 021 150 A1, the problem on which the present
invention is also based is described in detail. This is, specifically,
the ability to detect by use of an electronic control unit whether the
driver of a vehicle equipped with a driver assistance system, and
particularly with a driver assistance system that can automatically at
least slightly steer the vehicle, is sufficiently attentive and, in
particular, is capable of himself taking over the steering of the vehicle
at any time. As the vehicle is moving along, the moment imparted on the
steering wheel by the driver's hand will be measured, which can naturally
only result in an amount unequal to zero if the driver at least touches
the steering wheel. As long as the amount of the moment imparted by hand
is significantly greater than zero, a sufficient driver activity can be
inferred.

[0004] In the above-mentioned document, it is also described that, if no
hand-imparted moment of a magnitude greater than zero is detected for
only a brief time period, one does not immediately want to conclude that
there is a lack of driver activity. DE 10 2008 021 150 A1 therefore
describes a special method as to how, for a certain time period, the
evaluation can advantageously take place with respect to the
hand-imparted moment measured successively several times during that
time. Naturally, other methods are also contemplated which may
essentially lead to a comparable result, one of which will be briefly
described together with the present invention.

[0005] However, the latter, specifically a different computing sequence or
control sequence than that described in DE 10 2008 021 150 A1 is not the
essential content of the present invention. It is rather the object of
the present invention to further develop a method of detecting a lack of
driver activity at the steering wheel of a moving motor vehicle such that
the precision of the method will be further increased. As a result of the
increased precision, a low number of false alarms because of an
unnecessarily detected, only apparently lacking driver activity is to be
set off, as well as, in cases in which there actually is no sufficient
driver activity, such a lack of driver activity will be reliably detected
in a timely manner.

[0006] This object is achieved by the following: should, in the case of a
multiple successive falling-below a threshold value by current values of
a magnitude of a moment imparted by hand, a lack of driver activity be
inferred, the amount of the threshold value will be a function of the
surface condition, particularly of the degree of unevenness, of the
roadway traveled. Advantageous embodiments are described and claimed
herein.

[0007] According to the invention, the threshold value, with which a, or
the so-called, magnitude of a moment imparted by hand, which, for example
or preferably, may be the amount of the measured moment imparted by hand,
is compared, is not constant but depends on an essential marginal
condition which is of a not negligible significance for an inference of a
sufficient or lacking driver activity solely from the magnitude of the
moment imparted by hand. According to the invention, the surface
condition or the surface quality of the roadway should be considered, in
which case the most essential influence factor when taking into account
the road quality or the road condition, is the evenness or unevenness of
the roadway. It was specifically recognized that, for a roadway which has
the tendency to be uneven and, for example, has a plurality of
cross-grooves and/or longitudinal grooves or fairly small potholes, for a
determination of a sufficient driver activity, a moment imparted by hand
should be required whose amount should be larger than when the vehicle is
traveling on an absolutely even road, for example, formed by smooth
asphalt. In the case of a good surface condition of the road that is also
distinguished by a low level of unevenness, in particular, of small
dimensions, a significantly lower threshold value for the magnitude of
moments imparted by hand can therefore be set than in the case of a poor
road condition which may be characterized, for example, by a plurality of
fairly small or fairly large potholes. However, it is explicitly pointed
out that the term "surface condition of the road" is not limited to the
"unevenness" or "evenness" characteristic, but different threshold values
may also be provided as a function of the coefficient of friction between
the road and the wheels or tires of the vehicle. It is known that this
coefficient of friction can be estimated with sufficient precision.

[0008] In principle, various possibilities exist for detecting the surface
condition of the road. One possibility is an automatic optical analysis,
for example, by analyzing camera images of the road, or by, for example,
laser beam or ultrasound scanning; the latter also being included in the
concept of optical analysis. However, basically further methods are also
known, for the purpose of which reference is made to the documents
mentioned at the outset. Thus, for example, a so-called degree of
unevenness of the road can be derived from a measured vertical
acceleration in the wheel suspension (for example, in the shock absorber)
of the vehicle. As an alternative or in addition, it is also contemplated
to derive the degree of unevenness of the road from deceleration and/or
acceleration signals of at least one wheel of the vehicle, which can be
obtained from the rotational wheel speeds. Within the scope of such an
analysis, corresponding sensor signals can basically be subjected
particularly to a low-pass filtering, and/or the signal noise can be
evaluated. Independently of which method is used for detecting the road
condition, the detected road condition can then be classified, and a
threshold value for the magnitude of the moment imparted by hand can then
be selected, which threshold value is assigned to this classification and
with which the successively determined values of the magnitude of the
moment imparted by hand are compared.

[0009] Such a comparison of successively determined values of the
magnitude of the moment imparted by hand with the current threshold value
preferably takes place for a certain time period while the vehicle is
moving, so that, only if several successive measured values of the
magnitude of the moment imparted by hand are below the relevant threshold
value, a lack of driver activity is inferred. If, in contrast, a
determined value of the magnitude of the moment imparted by hand exceeds
a pertaining minimal value, preferably sufficient driver activity will be
inferred and, as a result, a new series of successive measurements of the
moment imparted by hand will be started, in which case the preceding
measurements (before that measured value that has exceeded the minimal
value) are not taken into account for the detection of a lack of
activity. With the exceeding of the above-mentioned minimal value by a
current value of the magnitude of the moment imparted by hand, a newly
indicated time period is therefore triggered or started. Here, it should
be explicitly pointed out that the mentioned time period does not have to
be a firmly predefined duration but can also be set, for example, by a
certain number of successive measurements of the moment imparted by hand.
As far as the mentioned minimal value is concerned, the latter may be
equal to the above-mentioned threshold value, or, as an alternative,
differ from the latter. It may also be provided that sufficient driver
activity can be inferred and therefore a new series of successive
measurements of the moment imparted by hand can be started only if the
magnitude of the moment imparted by hand continuously exceeds its
assigned minimal value during a certain time period. This defined
duration may be constant or variable; in the latter case, this duration
may be a function of the surface condition of the traveled road. In
addition, the above-mentioned minimal value that has to be exceeded so
that a sufficient driver activity can be inferred may also be a function
of the surface condition, particularly of the degree of unevenness of the
traveled road.

[0010] According to an advantageous further development, the length of an
above-mentioned time period within which several successive measurements
of the moment imparted by hand are carried out before, in the event of a
lasting falling below the threshold value, a lack of driver activity is
inferred, and/or the length of the mentioned time period during which
successive values of the magnitude of the moment imparted by hand have to
exceed the minimal value so that a new series of successive measurements
of the moment imparted by hand is started, may be depend on the driving
speed of the vehicle. Normally, the time that elapses between a first and
a second measurement of the moment imparted by hand will be constant and
will be dependent on the clock pulse period of a CPU or the like provided
in an electronic control unit in which the method according to the
invention is implemented. During a longer time period, in which each
measured magnitude of the moment imparted by hand has to be lower than
the mentioned threshold value so that a lack of driver activity is
inferred, a larger number of measured values of the moment imparted by
hand is therefore considered than during a shorter time period. During a
longer time period, it is therefore more probable that the driver
actively operates the steering wheel during this time period and that a
magnitude of the moment imparted by hand is therefore detected which
exceeds the mentioned minimal value. Since, in the case of a lower
driving speed of the vehicle, a brief inactivity of the driver naturally
has a lower risk potential than at a higher driving speed of the vehicle,
the above-mentioned time period, within which successively determined
values of the magnitude of the moment imparted by hand are compared with
a threshold value and in which case, when all values of the magnitude of
the moment imparted by hand are below the threshold value within this
time period, a lack of driver activity is inferred, may be longer at low
driving speeds than at higher driving speeds of the vehicle.

[0011] For example, at a driving speed of 10 km/h, this mentioned time
period may be in the order of 5 seconds and, at a driving speed of 40
km/h, may amount to only 2 seconds. A linear interpolation, for example,
is also contemplated between these example values. It is also explicitly
pointed out that, instead of a predefined time period, it may naturally
also be predefined how many successive measured values of the moment
imparted by hand or values of the magnitude of the moment imparted by
hand derived therefrom have to be positively checked for a falling below
the threshold value before a lack of driver activity can be inferred.
Such a predefined number of measured values also may be variable, and
particularly be a function of the driving speed of the vehicle and should
therefore in the present case be included in the term "variable time
period" or the time period dependent on the driving speed of the vehicle.

[0012] As mentioned above, the amount of the factually measured moment
imparted by hand can be used as the above-mentioned magnitude of the
moment imparted by hand. However, as an alternative, the use of the
gradient of the moment imparted by hand, i.e. the time-related derivation
of the moment imparted by hand or a use of the rate of change of the
moment imparted by hand is also possible, as indicated in DE 10 2008 021
151 A1. A further increase of the precision of the method according to
the invention can be achieved if, in addition to the amount of the moment
imparted by hand as the first magnitude of the moment imparted by hand,
the gradient of the moment imparted by hand is taken into account as a
further, second magnitude of the moment imparted by hand. Only in the
event that, in several successive measurements, the amount of the first
magnitude of the moment imparted by hand does not exceed the first
threshold value dependent on the road condition, and that the second
magnitude of the moment imparted by hand does not exceed a second
threshold value provided for this magnitude, will a lack of driver
activity be inferred. In this case, the threshold value for the second
magnitude of the moment imparted by hand may be constant or may also be a
function of the road condition or of the surface condition of the
traveled road.

[0013] When checking two (or more) different magnitudes of the moment
imparted by hand with respect to falling below a respectively assigned
threshold value within a predefined, preferably variable time period,
preferably as early as when only one of these magnitudes of this moment
imparted by hand exceeds its pertaining threshold value, a new series of
successive measurements of the moment imparted by hand (and thereby with
a new time period) will be started, so that the preceding measurements
are not taken into account for the detection of a lack of driver
activity. At this point, it should again be explicitly pointed out that
it is not absolutely necessary to use a firmly predefined or variable
time period for checking successive values of the magnitude(s) of the
moment imparted by hand with respect to their threshold value. The number
of successive measured values of the moment imparted by hand may rather
also be defined, in which case, this predefined number may also be a
function of the driving speed of the vehicle.

[0014] Other objects, advantages and novel features of the present
invention will become apparent from the following detailed description of
one or more preferred embodiments when considered in conjunction with the
accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

[0015]FIG. 1 is a simplified block diagram of a vehicle in which the
method according to the invention may be carried out;

[0016] FIGS. 2a-2c are exemplary flow charts illustrating the continuous
measurement of the moment imparted by a driver on a steering wheel, the
measurement of driving speed, and the determination of a characteristic
surface number representing wood roughness, respectively; and

[0017]FIG. 3 is a flow chart illustrating an exemplary method according
to the invention.

DETAILED DESCRIPTION OF THE DRAWINGS

[0018]FIG. 1 is a very schematic view of the two steerable front wheels
1a and 1b as well as of the two rear wheels 2a and 2b of a vehicle. A
rotational speed sensor 3 is assigned to each wheel 1a, 1b, 2a, 2b. Their
sensor signals are fed to an electronic control unit ESP, in which, among
others, an electronic vehicle stability program is implemented that is
known to a person skilled in the art. The steerable front wheels 1a, 1b
can be steered by way of a rack-and-pinion steering system 4, which is
also known to a person skilled in the art and whose schematically
illustrated steering rack 4a can be transversely displaced according to
the direction of the arrow 5 in order to adjust a desired wheel toe at
the front wheels 1a and 1b. The driver of the vehicle causes this
transverse displacement of the steering rack 4a by way of his steering
wheel 4b, which by way of a steering spindle 4c and a steering gear 4d,
in which, for example, also an electric-motor-driven power assistance
device may be integrated, correspondingly acts upon the steering rack 4a.
A torque sensor 6 is integrated in the steering spindle 4c or another
suitable element of the steering system 4, by which torque sensor 6, the
moment or torque by which the driver holds or rotates the steering wheel
4b can be measured. In the following, this torque will also be called a
"moment imparted by hand".

[0019] As illustrated in FIG. 2a, the amount of the moment imparted by
hand to the steering wheel 4b, that is, of that torque by which the
driver keeps a firm hold on the steering or rotates it at least slightly,
is continuously measured. This measured value is offset-corrected, which
results in a first magnitude of the moment imparted by hand MH used
subsequently, and the so-called gradient of the moment imparted by hand
is determined from this magnitude of the moment imparted by hand MH
by derivation with respect to time. The high-frequency parts are removed
from this last-mentioned signal by low-pass filtering, which results in a
second magnitude of the moment imparted by hand GH used
subsequently.

[0020] Parallel thereto, according to FIG. 2c, a characteristic surface
number representing the roughness of the road and thus the surface
condition of the road is determined from the rotational speeds of the
vehicle wheels continuously measured by way of the rotational speed
sensors 3 by low-pass filtering and further computing steps (in the
present case in the control unit ESP), which characteristic surface
number is characteristic of the quality of the currently present road
section. This information is transmitted to a further electronic control
unit ECU, in which the method according to the invention is implemented.
By means of the current characteristic surface number, a threshold value
MSW for the moment imparted by hand basically explained above for
the first magnitude of the moment imparted by hand MH or a further
(analogously basically already explained) threshold value GSW for
the gradient of the moment imparted by hand or for the second magnitude
of the moment imparted by hand GH are determined in the ECU. These
threshold values MSW and GSW are stored as tables in the
electronic control unit ECU as a function of the characteristic surface
number.

[0021] Also parallel thereto, as shown in FIG. 2b, it is queried whether
the driving speed v of the vehicle is above a minimal value vmin
because only above a low speed of, for example, 1.0 km/h does it have to
be checked whether the driver is firmly holding the steering wheel or is
controlling it. If the answer is in the affirmative, the control unit ECU
will operate as illustrated in FIG. 3 and explained in the following.

[0022] Referring to FIG. 3, from a point in time t=0, it is first checked
in the circle shown on the left-hand side whether the first magnitude of
the moment imparted by hand MH is smaller than the pertaining
threshold value MSW, and it is checked parallel thereto in the
circle shown on the right-hand side whether the second magnitude of the
moment imparted by hand GH is smaller than the pertaining threshold
value GSW. This checking may represent a quasi snapshot or may
extend over a very brief time period of several fractions of a second. If
the answers to these two parallel queries are negative; i.e. either when
a moment imparted by hand MH is present that is greater than the
pertaining threshold value MSW or a gradient of the moment imparted
by hand GH is present that is greater than the pertaining threshold
value GSW, the respective timer tn (for the left-hand circle)
or ti (for the right-hand circle) remains at the value t=0.

[0023] However, should at least one of these parallel queries have been
answered or be answered in the affirmative, the respective timer tn
or ti would be increased by one increment, whereupon it is checked
whether the respective timer has already reached a maximal value
tmax. If that is not so, it will be newly queried whether the first
or second magnitude of a moment imparted by hand MH or GH is
lower than the respective threshold value MSW or GSW.

[0024] If a predefined maximal value tmax for the timers was or is
exceeded by the above-mentioned increase of one of the two timers tn
or ti, it will be determined that the pertaining magnitude of the
moment imparted by hand (MH or GH) is too low. It will then be
checked whether the respective other magnitude of the moment imparted by
hand (i.e. in that case, GH or Mx) is also too low. If the answer is
in the affirmative, a warning is emitted which indicates that there is a
reasonable inference that the driver is not holding the steering wheel 4b
in a sufficiently firm manner. However, if the answer to the
last-mentioned query is negative, the current monitoring will be
continued as described.

[0025] Naturally, numerous modifications of the method described so far by
way of the attached exemplary figures are contemplated, several
possibilities being discussed above as to how these modification may be
constructed. The detailed sequence of the method is also not to be
incorporated into the claims but, as described in detail, it is claimed
that at least one of the above-mentioned threshold values (MSW or
GSW) for one of the above-mentioned magnitudes of the moment
imparted by hand (MH or GH) is a function of the surface
condition, particularly the degree of unevenness of the road or of the
roughness of the road.

[0026] The foregoing disclosure has been set forth merely to illustrate
the invention and is not intended to be limiting. Since modifications of
the disclosed embodiments incorporating the spirit and substance of the
invention may occur to persons skilled in the art, the invention should
be construed to include everything within the scope of the appended
claims and equivalents thereof.